1. Related Applications
This application is an improvement of my copending U.S. application Ser. No. 08/161,847 filed 6 Dec. 1993 for a UNIBODY ULTRASONIC TRANSDUCER.
2. Field of the Invention
The present invention relates to ultrasonic transducers of the type employed to bond two metallic elements together. More specifically, the present invention relates to a novel ultrasonic transducer of the type used on automatic wire bonders and ultrasonic bonding machines employed in the semiconductor industry.
3. Description of the Prior Art
Heretofore, ultrasonic transducers have been employed to bond fine wires to semiconductor pads and to the leads on lead frames or carriers to form electrical interconnecting gold and/or aluminum wires. Gold wires will bond to gold pads and leads using both pressure and heat to form a thermal compression bond. Gold wires will bond to the same gold pads or leads faster when ultrasonic scrub assist is added to the pressure and heat to form a thermosonic bond.
There can be found numerous academic opinions in the field of thermosonic fine wire bonding which advocate a single best frequency for making thermosonic wire bonds, however, manufacturers of automatic wire bonding machines and their customers who use such bonding machines to make highly reliable wire bonds have not standardized on the single best frequency. When more than one frequency is desired or needed, it has been necessary to change both the transducer and the generator to provide a different resonance frequency and this incurs a substantial downtime loss.
Heretofore, manufacturers of ultrasonic transducers used for fine wire bonding have offered standard fixed frequency generators and transducers. The fixed frequency transducers are provided with a mounting flange fixed at a zero displacement node when operated at the designed resonance frequency. When such prior art fixed frequency transducers are driven at multi (harmonic) frequencies of the designed fixed frequency, several problems arise which have prevented such prior art transducers from being useful at the higher harmonic frequency as will be explained in greater detail hereinafter.
It would be desirable to provide an ultrasonic transducer that is operable equally well at two or more fixed resonance frequencies in the range of frequencies that are useful for fine wire bonding operations. These frequencies presently extend from high sonic frequencies through the range of 300 kilohertz.